Field of the Invention and Description of the related art
Non-electrical pH probes and pO.sub.2 probes based on fiber optics and a dye indicator are known. Such devices are described fully in an article entitled "Fiber Optic pH Probe for Physiological Use" by Peterson and Buckhold which appeared in Analytical Chemistry, Vol 52, No. 6, May 1980 at pp. 864-869 and in a thesis entitled A Fiber-Optic Probe For Intravascular Blood Gas Monitoring submitted to the University of Minnesota in November 1988 by Jeffrey A. Schweitzer. These devices and compositions used in them are also described in U.S. Pat. Nos. 4,194,877; 4,200,110 and 4,476,870. All of these references are incorporated herein by reference.
This type of probe is based on the color change an indicator dye undergoes with varying conditions. For example, in a pH probe using phenol red, the dye exists in two forms over a certain pH range, exhibiting two different light absorption spectra. As the pH of a solution to which the probe is exposed varies, the optical absorbance varies in proportion to the change in pH. Operation is based on optically detecting the color change of the dye by fiber optic means as pH varies.
Heretofore, the indicator dye has been bound to an acrylic polymer composition, the dye being present with the monomer during the polymerization procedure. This prior art composition is referred to herein generally as a "acrylamide homopolymer". Unfortunately, the acrylamide homopolymer compositions have not been as stable as desired and have exhibited undesirable drift in pH indication and inaccurate indication over various ionic strength ranges. It is an object of this invention to provide a polymer dye composition which is improved in respect to these characteristics.